Longtime U.S. diplomat Richard C. Holbrooke, whose relentless prodding and deft maneuvering yielded the 1995 Dayton peace accords that ended the war in Bosnia - a success he hoped to repeat as President Obama's chief envoy to Afghanistan and Pakistan - died Monday in Washington of complications from surgery to repair a torn aorta. He was 69.

A foreign policy adviser to four Democratic presidents, Mr. Holbrooke was a towering, one-of-a-kind presence who helped define American national security strategy over 40 years and three wars by connecting Washington politicians with New York elites and influential figures in capitals worldwide. He seemed to live on airplanes and move with equal confidence through Upper East Side cocktail parties, the halls of the White House and the slums of Pakistan.

Obama praised him as "a true giant of American foreign policy who has made America stronger, safer and more respected. He was a truly unique figure who will be remembered for his tireless diplomacy, love of country, and pursuit of peace."

Secretary of State Hillary Rodham Clinton said in a statement that the United States "has lost one of its fiercest champions and most dedicated public servants."

The death could have a profound impact on the administration's efforts to implement aspects of its strategy for the war in Afghanistan, which relies not just on military gains but development assistance and diplomatic initiatives with the governments in Kabul and neighboring Pakistan that had been his principal focus.

Mr. Holbrooke's expansive career began in Vietnam's Mekong Delta, where he served as a field officer, and included appointments as the U.S. ambassador to the United Nations and as one of the youngest assistant secretaries of state in U.S. history. When Republicans were in power, he was a banker, a journalist and a best-selling author.

His most prominent role was as a presidential wartime problem solver, to which Mr. Holbrooke applied an unwavering energy, a flair for diplomatic improvisation and a hard-charging style that could yield dramatic breakthroughs but also generate bitterness and enmity, even among his American teammates.

Although the consequences of his forceful personality were laid bare in his efforts to stabilize Afghanistan and Pakistan, leading to tense disagreements with leaders of those nations and fellow U.S. officials, Mr. Holbrooke never stopped trying to address the insurgencies that threaten both countries.

Over the past year, he maintained a peripatetic existence, often subsisting on just a few hours of sleep at night, as he globe-trotted to shore up allied support for the war and a costly reconstruction program.

"As anyone who has ever worked with him knows - or had the clear disadvantage of negotiating across the table from him - Richard is relentless," Obama said earlier Monday at a State Department holiday reception. "He never stops. He never quits. Because he's always believed that if we stay focused, if we act on our mutual interests, that progress is possible. Wars can end. Peace can be forged."

A defining moment

Mr. Holbrooke's most significant achievement occurred in 1995, at Wright-Patterson Air Force Base outside Dayton, Ohio, when he forged a deal among bitter rivals to end three years of bloody sectarian war in the former Yugoslavia that killed an estimated 100,000 people.

The talks, which lasted 20 days, would not have taken place had he not spent three months shuttling among the principal Serbian, Croatian and Muslim leaders to cajole, arm-twist and threaten, while also employing the bone-jarring power of U.S.-led NATO airstrikes.